Presently, U.S. cable systems deliver hundreds of channels to some 60 million homes, while also providing a growing number of people with high-speed Internet access.
In 1989, General Instruments demonstrated that it was possible to convert an analog cable signal to digital and transmit it in a standard 6-MHz television channel. Using Motion Picture Expert Group (MPEG) compression, CATV systems installed today can transmit up to 10 channels of video in the 6-MHz bandwidth of a single analog channel. When combined with a 550-MHz overall bandwidth, this allows the possibility of nearly 1,000 channels of video on a system. In addition, digital technology allows for error correction to ensure the quality of the received signal.
In current Hybrid fiber-coaxial systems, a fiber optic network extending from the operator's central office carries all video channels out to a fiber optic node which services any number of homes ranging from 1 to 2,000 homes. From this point, all channels are sent via coaxial cable to each of the homes. Note that only a percentage of these homes are actively watching channels at a given time. Rarely are all channels being accessed by the homes in the service group.
In a switched video (SV) system, the unwatched channels do not need to be sent. In cable TV systems in the United States, equipment in the home sends a channel request signal back to a distribution hub (also referred to as a Switched Digital Video server or SDV server). If a channel is not currently being transmitted on the coaxial line, the distribution hub allocates a new Quadrature Amplitude Modulation (QAM) channel and transmits the new channel to the coaxial cable via the fiber optic node. For this to work, the equipment in the home must have two-way communication ability. Switched video uses the same mechanisms as Video on Demand (VOD) and may be viewed as a non-ending video on demand show that any number of users may share.
For a switched video system to work on cable systems, all digital television users in a subscription group must have devices capable of communicating to the distribution hub in a compatible manner. Switched video is sometimes abbreviated as SDV for switched digital video, or SVB for switched video broadcast.
Switched Digital Video technology enables Multiple System Operators (MSOs) to offer consumers a wider variety of programming while effectively managing Hybrid Fiber/Cable (HFC) network bandwidth. From a business perspective, SDV offers MSOs a number of key benefits. First, SDV is a cost-effective bandwidth management tool that immediately reduces HFC bandwidth requirements compared with traditional “linear” content delivery. Second, the SDV system bandwidth scales as a function of viewership rather than as a function of programs offered. Therefore SDV gives MSOs the ability to offer new programming tiers including premium sports, ethnic and other niche programming that drive customer retention and may drive new revenue through premium subscriptions. Third, SDV technology enables channel change times that are comparable to those in today's networks, so SDV services can be delivered transparently to consumers without a change in the television viewing experience, thereby eliminating concerns about viewer adoption that have plagued other new services. Finally, SDV systems capture very detailed viewership data in a secure manner that protects consumer privacy. This powerful information is used to optimize system performance, but it can also be used to optimize program offerings and lineups, and to enhance targeted advertising.